1. Field of the Invention
The present invention relates to a directional electric device, in particular, an antenna which is carried on board a vehicle or the like.
2. Description of the Related Art
In recent years, for example, with the spread of introduction of car information equipment such as the introduction of a two-way information terminal into a car navigation device, introduction of an automatic rate collection system, and the like, the number of car on-board antennas used shows a tendency to increase.
Conventionally, these car on-board antennas have been carried on board the inside and outside of a car body according to their individual systems. For example, a GPS (Global Positioning System) antenna for car navigation is in most cases installed on the roof of the car body and is connected by a coaxial cable to the main body of a car navigation device installed in the inside of the car. Also, an antenna for a radio wave beacon or an antenna for an optical beacon, which is used in a VICS (Vehicle Information and Communication System), is installed on an instrumental panel and is connected by a cable to the main body of the car navigation device. Further, an antenna for an automatic rate collection system is installed on the instrumental panel and is connected by a coaxial cable to the main body of the car navigation device.
However, in the above-mentioned conventional method, there are found several problems as follows:
(1) Since the antennas are installed on the car body or instrumental panel, they are not fit to be seen and, sometimes, can make a driver uncomfortable while driving the car.
For example, the antenna installed on the instrumental panel casts its shadow onto the windshield of the car, which provides an obstacle to driving.
(2) Cables for connecting the respective antennas to the receiving part of the car navigation device and connectors used for such cables are necessary in number corresponding to the number of the antennas used, which increases the cost of the car navigation device.
Further, installation of these antennas is an option and is carried after completion of assembling of the car, which also raises the following problems in the wiring operation:
(3) Because wiring for the antennas is arranged on the instrumental panel or along the upholstery of the car, such wiring is not fit to be seen.
(4) When arranging the antenna wiring within the upholstery (for example, within the instrumental panel) in order to improve the above-mentioned poor wiring, the upholstery. must be removed once and the operation to remove the upholstery takes time and labor.
In addition, conventionally, as a receiver unit for use in a navigation system or the like carried on board a vehicle such as a car or the like, there is known a receiver unit 101 having such a structure as shown in FIGS. 21 and 22. The illustrated receiver unit 101 includes a metal case 102 and antennas 103, 104 each of a flat-surface type, that is, in the receiver unit 101, normally, in order to prevent the deterioration of the performance of the antennas, the antennas 103 and 104 are disposed on the upper surface portion of the metal case 102.
Besides, between a substrate part 105, which is disposed on the upper portion of the receiver unit 101 and also on which circuitry is formed, and the upper surface of the case 102, there are packaged or mounted other necessary parts 106. Further, when there is a position restriction that a given clearance must be provided between the antennas 103, 104 and the substrate part 105, the antennas 103 and 104 are respectively mounted on their corresponding given sub-substrate 108 and 109 and are also connected to their corresponding connecting connectors 112 respectively serving as antenna connecting parts on the substrate 105 side by use of their respective cables 110 and connectors 111.
Further, reference characters 114 and 115 respectively designate upper portion cover bodies which are mounted on the upper surface portion of the case 102 in such a manner that they respectively cover their corresponding antennas 103 and 104, while the upper portion cover bodies 114 and 115 respectively include a pair of engaging projection pieces 114a and 115a which are provided in the lower end edge portions thereof. On the other hand, the case 102 includes two openings 116 and 117 which are respectively formed in the upper surface of the case 102, while the two openings 116 and 117 respectively include securing portions 118 and 119 respectively formed in the peripheral edge portions thereof. Thus, the securing projection pieces 114a and 115a of the two upper portion cover bodies 114 and 115 are respectively inserted into and secured to securing holes respectively formed in the securing portions 118 and 119, whereby the upper portion cover bodies 114 and 115 can be fixed and held in such a manner that they are prevented against removal. Further, due to such fixation of the upper portion cover bodies 114 and 115, the antennas 103 and 104 can be positioned and fixed respectively.
However, in the above-mentioned conventional method for connecting the antennas 103 and 104 to the substrate part 105, there are required the sub-substrates 108, 109, cables 110, and connectors 111 separately, that is, the number of parts necessary is large, which results in the high cost of the antenna device.
In addition, in the above conventional method, when mounting the antennas 103 and 104 onto the substrates 108 and 109, as shown in FIG. 23, there is employed a technique in which they are bonded using a double-side adhesive tape 121. However, in such bonding operation, there are required an operation to remove a protection film from the double-side adhesive tape 121 and an operation to bond the double-side adhesive tape 121 to the antennas 103 and 104 as well as to the sub-substrates 108 and 109. For this reason, the bonding operation is troublesome and is poor in efficiency. Further, when a foreign body is present between the double-side tape 121 and antennas 103, 104 and/or between the double-side tape 121 and sub-substrates 108, 109, there is a fear that the double-side tape 121 can be removed due to vibration or the like. In the bonding operation, the double-side tape 121 must be bonded with the directivities of the antennas 103 and 104 taken into account.